Semiconductor wafers are frequently transferred from one processing station to another via cassettes that have a series of parallel slots each of which receives and holds a single wafer. In some cases, the cassettes are sized and shaped to receive and hold a film frame or similar device upon which the wafer has been mounted for processing in sawing and die attach equipment. Wafers, or the film frames upon which wafers have been mounted, are typically loaded into and unloaded from a cassette automatically by the processing machine or another robotic mechanism. Although automated cassette transport systems are known in the industry, most cassettes are transferred from one processing station to another by hand. The hand transportation of the cassettes significantly increases the risk that the cassettes will be mishandle and the wafers damaged. Conventional film frame and wafer cassettes have several disadvantages that make the wafers held therein particularly susceptible to accidental damage. In some cassettes, a substantial portion of the film frame upon which the wafer is mounted extends outside one or both ends of the cassette. The exposed portions of the film frame may be inadvertently bumped, snagged or otherwise disturbed during handling thus increasing the risk of damage to the wafer. Similarly, much of the top wafer in a conventional cassette is exposed and, consequently, the surface of the top wafer is often scratched or otherwise damaged during transfer or other handling operations.
Another problem associated with the handling of conventional cassettes is the excessive lateral movement of the frames/wafers when the cassette is tilted. Conventional cassettes allow the film frames to move laterally between 1/2 inch and 1 1/2 inches when the cassette is tilted. The momentum attained by the frames/wafers as they slide through this distance may be sufficient to overcome the retaining mechanism, particularly if the cassette is abruptly bumped or jarred. A further problem that has been observed in the use of conventional film frame and wafer cassettes is that the retaining mechanism can and sometimes is overridden by the human operator/handler. That is, the retaining comb is locked into the open position. This is particularly a problem during operations in which the cassettes are loaded by hand. If the operator fails to "unlock" the retaining comb after the cassette is loaded, then the frames/wafers will readily slide out of the cassette. The cost associated with losing or substantially damaging even one wafer is a significant.
The present invention is directed to the resolution or amelioration of the above stated problems observed with regard to some types of conventional film frame and wafer cassettes.